Praise be to Allah.
It is permissible for a worshipper to use anything as a sutrah [an object placed in front of him to “screen” him whilst he is praying], even if it is an arrow, because the Prophet (peace and blessings of Allaah be upon him) said: “When any one of you prays, let him place a sutrah for his prayer, even if it is an arrow.” Narrated by Ahmad, 14916; classed as saheeh by al-Albaani in al-Silsilah al-Saheehah, 2783. The scholars even said: He can screen himself with a thread or the edge of the rug. Indeed it says in the hadeeth that the Prophet (peace and blessings of Allaah be upon him) said whoever cannot find a stick, let him draw a line, as it says in the hadeeth of Abu Hurayrah, according to which the Prophet (peace and blessings of Allaah be upon him) said: “When any one of you prays, let him face towards something, and if he cannot find anything, let him use a stick, and if he does not have a stick, let him draw a line, then it will not matter whatever passes in front of him.” Narrated by Imaam Ahmad. Ibn Hajar said in Buloogh al-Maraam: Those who said that this hadeeth is weak are incorrect; rather it is hasan.
All of this indicates that the sutrah does not have to be big, rather it is sufficient for it to be something that indicates that it is serving as a screen.
There is no doubt that shoes are big and three dimensional, but I think that they should not be used as a sutrah, because shoes are customarily regarded as dirty, and you should not have them in front of you, when you are standing before Allaah. Hence the Prophet (peace and blessings of Allaah be upon him) forbade worshippers to spit in front of them so that the sputum would be in front of them, and he (peace and blessings of Allaah be upon him) said: “For Allaah is in front of him [the worshipper].” Narrated by al-Bukhaari, 406.
Fataawa Ibn ‘Uthaymeen, 13/326.
See also the answer to question no: (40865).